linux-kernel - Re: [PATCH] Refactor hypercall infrastructure

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Date:	Fri, 14 Sep 2007 13:53:26 -0700
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Anthony Liguori <aliguori@...ibm.com>
CC:	kvm-devel@...ts.sourceforge.net, Avi Kivity <avi@...ranet.com>,
	Ingo Molnar <mingo@...e.hu>, Dor Laor <dor.laor@...ranet.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] Refactor hypercall infrastructure

Anthony Liguori wrote:
> This patch refactors the current hypercall infrastructure to better support live
> migration and SMP.  It eliminates the hypercall page by trapping the UD
> exception that would occur if you used the wrong hypercall instruction for the
> underlying architecture and replacing it with the right one lazily.
>   

I guess it would be pretty rude/unlikely for these opcodes to get reused
in other implementations...  But couldn't you make the page trap
instead, rather than relying on an instruction fault?

> It also introduces the infrastructure to probe for hypercall available via
> CPUID leaves 0x40000002.  CPUID leaf 0x40000003 should be filled out by
> userspace.
>   

Is this compatible with Xen's (and other's) use of cpuid?  That is,
0x40000000 returns a hypervisor-specific signature in e[bcd]x, and eax
has the max hypervisor leaf.

    J
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